In general, compositions containing alkali-soluble resins and, as the photosensitive material, naphthoquinonediazido compounds are used as positive photoresist compositions. For example, "novolak phenol resin/naphthoquinone-diazide-substituted compounds" are disclosed in U.S. Pat. Nos. 3,666,473, 4,115,128 and 4,173,470 and, as a more typical composition, an example of a "novolak resin/trihydroxybenzophenone-1,1-naphthoquinonediazidosulfonic acid ester formed from cresol formaldehyde" is disclosed in "Introduction to Microlithography" by L. F. Thompson (ACS Publishing, No. 219, pp 112-121).
The novolak resin which is used as the binder is able to dissolve in aqueous alkaline solutions without swelling and has a particularly high resistance to plasma etching when used as a mask for etching the image formed, and it is therefore particularly useful in this application. Furthermore, although the naphthoquinonediazido compounds used as the light-sensitive substances themselves act as dissolution inhibitors by reducing the alkaline solubility of the novolak resin, they are distinctive in that they produce alkali-soluble materials when degraded upon irradiation by light and in fact work to raise the alkali solubility of the novolak resin and, due to this major property change in light, they are particularly useful as the light-sensitive substance in a positive photoresist.
Hitherto, numerous positive photoresists containing novolak resins and naphthoquinone diazide-based light-sensitive substances have been developed and produced on the basis of such considerations with adequate results for line working up to widths of about 1.5 to 2 .mu.m.
However, the degree of integration of integrated circuits is ever increasing and it is becoming necessary to work extremely fine patterns, composed of lines with a width of less than 1 .mu.m, in the manufacture of ultra-large scale integrated and other such semiconductor boards. In such applications, there is, in particular, a need for a photoresist having a high sensitivity in terms of high resolving power, high-precision pattern reproduction whereby the pattern of the exposed mask is copied accurately, and high producibility which, at present, the conventional positive photoresists mentioned above cannot satisfy.